During the use of a multi-meter or other electronics test equipment, if the test leads are incorrectly inserted, this will damage the equipment. Based on experience in repairing damaged meters, over 50% of the cases are caused by the incorrect insertion of the test leads. As a result, some manufacturers added warning buzzers or other sound devices to alert the user that the meter has been damaged. Unfortunately, these warning devices are activated only after the equipment has been damaged, therefore it cannot prevent the meter from being damaged.